Method of spraying

ABSTRACT

Improved performance of known techniques of spraying liquids to form extremely dense liquid sprays or aerosols can be obtained by pre-saturation of the carrier gas at a given location before final introduction of the product to be aerosolized into the spraying system.

Unlted States Patent 119 Babington Feb. 5, 1974 [54] METHOD OF SPRAYING 2,143,817 1/1939 Longdinm, 239/428 x [76] Inventor: Robert S. Babingto 3 ng e 3,606,159 9/1971 Sutton 239/426 X Ave., McLean, Va. 22101 Primary Examiner-Richard A. Schacher Flled? May 22, 1972 Attorney, Agent, or Firm-Gardner, Sixbey, Bradford 21 Appl. No.: 255,686 and Carlson [52] US. Cl ,239/8, 239/422, 239/428 [57] ABSTRACT [51] Int. Cl B05b 7/00 [58] Field of Search... 239/428 346, 422, 426, 430, P Permmance l f Spray 239/429 8 338 ing l1quids to form extremely dense l1qu1d sprays or aerosols can be obtained by pre-saturation of the car- 56] References Cited .rier gas at a given location before final introduction of UNITED STATES PATENTS the product to be aerosohzed mto spraymg system.

5 Claims, 4 Drawing Figures 549,822 11/1895 Robertson 239/338 11' l l x. i. 1 2 4 11/ L\\\\\ g I 2 l 5 3 5 3 l l l A L A L METHOD OF SPRAYING BACKGROUND The subject matter herein dealt with is of general interest in the art of spraying. In particular, the method finds utility in the art of producing aerosolized products 'where it is desired to develop extremely fine particle sizes, on the order of ten microns or less, and to, additionally, produce a substantial number of such particles per given volume of carrier vehicle, usually a gaseous medium.

The present invention evolved from studies conducted to develop a spraying'system utilizing the principles of Babington et al U.S. Pat. Nos. 3,421,692 and 3,421,699 which principles have been utilized in burners, see U. S. Pat. No. 3,425,058 among others, humidifiers, see U. S. Pat. No. 3,425,059; mist lubrication of high speed drives, paint spraying and last but not least, medical nebulizers of the type disclosed in the application of Robert S. Babington filed of even date herewith.

Basically the Babington system involves flowing a liquid in thin film over a suitable surface which has a very small aperture therein and emitting a gas through the aperture traversing said film of liquid whereby miniscule droplets of liquidare lifted from the film while that portion of the film which is not atomized or nebulizedis permitted to flow beyond the aperture and generally collected for recirculation into the system.

The most simple basic device incorporating the Babington system ultimately evolved in the configuration shown in.U.S. Pat. No. 3,425,059 which device proved capable of producing sprays containing particles of very minute sizes. This fact immediately suggested that devices incorporating the Babington principle might have application in the medical field where it is most desirable to produce sprays or fogs of extremely high density, on the order of 10,000,000 to 15,000,000 liquid particles per cubic centimeter of carrier gas. Not only must the spray or fog be of high density, but the particle size must be as small as possible and preferably with a mass median diameter on the order of 4 5 microns.

Comparison of the Babington device with known pneumatic systems and the ultrasonictype wherein the liquid is introduced into carrier air by 'means of high frequency ultrasonic vibrations, indicated that even in its most rudimentary form, the Babington device showed the .potential of out-producing known pneumatic systems and further modification might well result in a pneumatic nebulizer capable of performing as well as an ultrasonic type but at substantially less initial and maintenance costs to the user.

THE INVENTION As a result of the encouragement generated by the comparisons outlined above, an object of the present .invention became the development of a method of spraying liquids capable of producing a fog or mist having particle sizes on the order of 4-5 microns and at densities at least on the order of 10,000,000 particles per cubic centimeter of carrier gas.

Another object of the invention is to provide a method of aerosolizing liquid medicants which can be directly inhaled into the respiratory tract.

Still a further object of the invention is to develop a method of aerosolizing liquids requiring high rrrist densities, small particle size and ample capacity measured in terms of usable mist per unit of time.

A further object of the invention is to provide a method of improving the output both in capacity and density of all known spraying or aerosolizing systems.

Still another object of the invention is to provide a method of producing aerosols by use of pneumatic spraying systems.

These and other objects of the invention, not necessarily set forth, but inherent therein are accomplished by a method of spraying comprising the steps of providing an aspirating chamber, providing a firstatomizing means in said chamber, providing a second atomizing device in said chamber in series with the first'atomizing device introducing aspirating airinto said chamber, passing over the series oriented atomizing devices, a carrier vehicle whereby the atomized particles from said first device are at least partially evaporated into the carrier vehicle prior to its point of contact with the atomized particles of said second atomizing device.

The overall result produced may be enhanced by passing the carrier vehicle through a trapchamber to trap out larger particles which collect as a result of their greater mass and momentum.

Having described the invention in general terms, the method will be more clearly understood from consideration of the following detailed description, reference being made to the attached drawings wherein:

FIG. 1 is a simple schematic view showing the method as applied to a conventional pneumatic atomizing device,

FIG. 2 is a view similar to FIG. 1 but showing atomizers of the Babington type incorporated in the device carrying out the present method,

FIG. 3 is a schematic view similar to FIG. 2 but substituting ultrasonic atomizing units in the system, and

FIG. 4 is a partial view disclosing a generic means for improving the results of known pneumatic systems, but illustrating in particular, use of the system disclosed in FIG. 2.

As shown in FIGS. 1, 2 and 3, there is provided a spray chamber 1, so called because its purpose is to direct the carrier vehicle, by'self aspiration or forced aspiration, in a given direction and to confine the carrier I vehicle in a limited area during introduction of the atomized or aerosolized substance thereinto from the spraying elements.

In FIGS. 1 and 2 the chambers l and 10 are selfaspirating. That is, the carrier-vehicle, in this case air or any known gas is drawn into the chamber through apertures 2 and 12 respectively by the action of theatomizing devices themselves, since both the FIG. 1 and FIG. 2 devices are pneumatic devices requiring discharge of the air under pressure to atomize the liquid substance to be atomized. In FIG. 1, the atomization is of the simple dual nozzle type wherein liquid is forced under pressure into pipe 3; a gas under pressure is introduced into pipe 5 and atomization of the liquid substance occurs because of the impact between liquid and gas streams. As a general rule the gas is under considerable pressure about 50 p.s.i. gage, hence the velocity of the gas stream is sufficient to cause flow of the atomized liquid in the exit direction through the chamber 1, i.e., to the right as viewed in FIG. 1.

At a given point, denoted by distance D, the flowing stream of atomized particles passes over and around a second atomizing device which may be duplicate of the first atomizing device having air nozzle 3' and liquid nozzle 5' where additional atomized substance is introduced into the carrier vehicle.

The carrier vehicle, in this case simply defined as a suitable gas, is drawn in through the aspirating ports 2 by the effect of the atomizing nozzles which causes a reduction in pressure within the chamber 1 adjacent the closed end. Hence, the carrier vehicleis drawn into the chamber through ports 2 and co-mingles with the sprayed substance at the first stage. The carrier vehicle which is now preconditioned, i.e., has absorbed some additional moisture and also carries some free liquid in aerosol form, which mixture is accelerated toward the second spray stage, i.e., toward the exit end of the chamber. In its passage to the exit, it is again exposed to an additional spray generator which introduces additional free liquid particles into the preconditioned carrier vehicle.

The description of the phenomenon which is believed to produce the improved results will be deferred for the moment, while the forms shown are considered, having in mind the phenomenon is common to all forms of devices capable of carrying out the improved method.

Thus, turning to the FIG. 2 form it will be seen that again the most simple manifestation of the invention comprises an aspirating chamber having a closed end 11 and an exit opening 13. Instead of the more conventional pneumatic atomizers the chamber 10 includes the so-called Babington atomizers utilizing the principles set forth in the aforementioned Babington et al US. Pat. Nos. 3,421,699 and 3,421,694. In this system comparatively low pressure atomizing gas is applied through conduits 15, 17 to a pair of serially arranged, horizontally aligned hollow plenum chambers in the form of spheres 16 and 18. The surfaces of the spheres 16 and 18 are flooded with the substance to be atomized, for example, water or a saline solution or any liquid substance having a soluble solid dissolved therein via conduits 22, 24 aligned with the tops of the spheres. The contour of the spheres and the rate of flow of the liquid is such that the substance forms a thin dynamically stressed film over each sphere. The spheres are provided with very small slots 25, 27 as described in said patents, from which the relatively low pressure air exits to traverse the film and in so doing very small droplets are lifted from the film and dispersed into the chamber. The remainder of the film is caught in catch basins 14, 19 and conveyed back into the liquid supply system by any suitable means (not shown) for recirculation.

Again, the gas emitted from apertures 25, 27 creates a velocity component toward the exit opening 13 with the result that aspiration of the carrier vehicle is effected through aspirating ports 12 adjacent the closed end 11 of the chamber 10.

Again, before consideration is given to an explanation of the discovered phenomenon, another arrangement for carrying out the invention will be described with reference being made to FIG. 3. Again, an aspirating chamber 20 is provided having an end 32 arranged for admission of air into the chamber. A pair of atomizing devices 34, 36 of theultrasonic type (i.e., atomization of the liquid is effected by high frequency vibrations) are serially arranged within the chamber 1. Because the atomization is effected by an ultrasonic technique, it is obvious that some additional means must be provided to induce the carrier vehicle flow through chamber 20. Various means can effect the desired result as will be apparent. However, for illustrative purposes, in FIG. 3 the means is shown as being a simple fan 38 driven by a motor v40 to cause air flow through the opening 42 in the end of chamber 20. Thus, the carrier vehicle, is caused to flow by what may be termed forced aspiration, through the chamber 20 and over the serially arranged atomization devices 34, 36.

In FIG. 4, there is disclosed a modification of the spray source which is applicable to any pneumatic nebulizer but, for simplicity is disclosed in combination with a Babington type of system. The modification consists of placing an impact means in the path of the spray generated at the nozzle or spherical surface. As shown the impactor 48 is affixed by a support 46 so as to be directly aligned with the aperture 25 in the spherical plenum chamber 16. Thus the small particles ofliquid lifted from the dynamic film of liquid surrounding the outside spherical surface of sphere or plenum chamber 16 are carried into direct contact with impactor 48 and, due to their momentum are further broken up upon contact with the impactor 48. In the form shown, the impactor 48 is a sphere. It has been found that this shape performs eminently well with the Babington system. However, it must be realized that other forms of impactor are considered within the scope of the disclosure and that the impactor size, configuration and position relative to the nebulizing stream and the nozzle is variable depending upon the pneumatic system used and therefore on stream velocity, particle for mation and the like.

METHOD AND THEORY OF OPERATION With basic means being disclosed for carrying out the intended process, the immediate question becomes one of what is the operation. By observation and comparative results it is believed that the process products improved results because a carrier vehicle normally will absorb at least a goodly portion of the small particles emanating from a spray source. It is believed this absorption occurs because the carrier vehicle is unsaturated, that is, its moisture content is such that the relative humidity of the carrier gas is below percent before it encounters the sprayed liquid produced at the first source of contact between spray and carrier vehicle.

Where a spray is generated having very small particles, it is these particles which are first absorbed or evaporated into the carrier vehicle to raise the moisture content or relative humidity thereof while the somewhat larger particles of spray are those which are physically carried along by the carrier vehicle. Much larger.

particles, influenced by gravitational or other forces, are not carried by the carrier vehicle and wet out on surrounding objects. A

If, then, the carrier vehicle is preconditioned, i.e., it is close to its saturation point when it encounters the spray, the smaller droplets are not absorbed at a rapid rate but are suspended in the carrier gas and remain in droplet form to the point of application. The discovery of this phenomenon gave rise to th conclusion that, if two spraying devices were arranged in series within a chamber such that the first device served to precondition the carrier vehicle, improved performance of any known spraying device could be anticipated since the physical number of suspended droplets of smaller size will be increased. It was also recognized that the most effective manner in carrying out the method was to place the serially-arranged spray units in a chamber such that the preconditioned carrier vehicle would be guided to the second or forward spray device from the first or rear spray device in completely preconditioned status with the result that the spray output of the second device is transported virtually in toto in usable droplet form. I

By way of explanation of the superior performance of this configuration of nebulizer, it is believed that with the use of a series of atomizing devices, the mist from the rear atomizer is entrained into that produced by the front atomizer. In this manner, thespray from the rear or first atomizer more effectively and efficiently fills. the voids between the liquid particles produced by the front atomizer. By contrast, when multiple sprays emit from a single atomizer, rather than in a series configuration, as disclosed herein, more turbulence occurs and the collision rate of liquid droplets is greater. Both of these factors cause agglomeration of particles and subsequent rain-out or deposition of particles within the nebulizer or distribution hose. For example, in a medical nebulizer, with a single atomizer design utilizing multiple slots, it is highly probable that a large nonrespirable particle (i.e., greater than 10 microns) will collide with a highly respirable particle of 2 or 3 microns, and prevent the smaller particle from negotiating the distribution hose and being inhaled by the patient. on the other hand, if the two droplets were produced in a series configuration, with the front atomizer producing the larger particle and the rear atomizer producing the smaller particle; it is highly probable that the small particle would be sucked into oneof the void spaces in the mist produced by the front atomizer. In so doing, it would be carried along through the distribution hose and add to the mist density produced by the total nebulizer configuration. By locating atomizers in series, the larger or non-respirable particles produced by the first atomizer in the series, never reach the spray plume of the forward or second atomizer, because their decaying trajectory causes them to rain-out. This serves to keep the nebulizer from becoming cluttered with non-respirable large particles, which in turn reduces the possibility of collision and agglomeration. In addition, by locating atomizers in series, the relative velocity of the spray particles produced by the individual atomizers is reduced. Thispromotes more efficient droplet entrainment which in turn allows more liquid particles to be transported per volume of carrier air.

In discussing the method and theory of operation thus far, mention has been made of only two atomizers in series. It should be understood that the method herein described can be used with any number of atomizing devices. As more atomizers are added so as to be traversed in series by the carrier gas, the density of the final aerosol produced, in terms of moisture content,

and/or liquid particles transported by a unit volume of carrier gas, will increase and approach the theoretical maximum density. Experimental data produced by various arrangements of serially oriented spray devices has shown that the aerosol density from multiple atomizers is substantially greater than that produced by a single atomizer.

Having thus described the invention indetail, it is obvious that various modifications, applications and changes will occur to those skilled in the art and falling within the spirit and scope of the appended claims, wherein:

What is claimed is:

1. A method of spraying'comprising the steps of providing a spray chamber, providing a first liquid atomizing means in said chamber, providing at least one-additional liquid atomizing device in said chamber in series with the first atomizing device, introducing carrier gas into said chamber so as to pass over the series oriented atomizing devices while confined within said chamber, simultaneously operating said atomizing devices to produce atomized liquid particles whereby the atomized particles from said first device are at least partially evaporated into the carrier gas prior to its passage over said additional atomizing devices and thereafter discharging said particle-laden carrier gas from said chamber.

2. The method of spraying defined in claim 1 wherein there is provided at least a pair of pneumatic atomizing devices and the gas aspirated through said chamber is provided by the venturi effect generated by said pneumatic atomizing devices.

'3. The method of spraying as defined in claim 1 wherein there is provided at least a pair of ultrasonic atomizing devices and said step of providing aspirating gas is effected by a separate gas moving device. I

4. The method of spraying as defined in claim 1 including the further step of impacting the atomized I spray from at least one of said atomizing devices to further reduce particle size of the substance being conveyed by the carrier gas..

5. A method of producing high density liquid sprays of particles on the order'of .10 microns or less comprising the steps of providing a moving stream of a carrier vehicle within a chamber, first introducing the liquid substance being sprayed into said carrier vehicle in atomized particle form whereby a portion of the particles are absorbed by said carrier vehicle while in said chamber and thereafter introducing additional amounts of the substance being aerosolized into the carrier vehicle in liquid particle form within said chamber, whereby the majority of particles last introduced into the carrier vehicle are retained and carried thereby to a point of i use in liquid particle form and discharging said particle- 

1. A method of spraying comprising the steps of providing a spray chamber, providing a first liquid atomizing means in said chamber, providing at least one additional liquid atomizing device in said chamber in series with the first atomizing device, introducing carrier gas into said chamber so as to pass over the series oriented atomizing devices while confined within said chamber, simultaneously operating said atomizing devices to produce atomized liquid particles whereby the atomized particles from said first device are at least partially evaporated into the carrier gas prior to its passage over said additional atomizing devices and thereafter discharging said particle-laden carrier gas from said chamber.
 2. The method of spraying defined in claim 1 wherein there is provided at least a pair of pneumatic atomizing devices and the gas aspirated through said chamber is provided by the venturi effect generated by said pneumatic atomizing devices.
 3. The method of spraying as defined in claim 1 wherein there is provided at least a pair of ultrasonic atomizing devices and said step of providing aspirating gas is effected by a separate gas moving device.
 4. The method of spraying as defined in claim 1 including the further step of impacting the atomized spray from at least one of said atomizing devices to further reduce particle size of the substance being conveyed by the carrier gas.
 5. A method of producing high density liquid sprays of particles on the order of 10 microns or less comprising the steps of providing a moving stream of a carrier vehicle within a chamber, first introducing the liquid substance being sprayed into said carrier vehicle in atomized particle form whereby a portion of the particles are absorbed by said carrier vehicle while in said chamber and thereafter introducing additional amounts of the substance being aerosolized into the carrier vehicle in liquid particle form within said chamber, whereby the majority of particles last introduced into the carrier vehicle are retained and carried thereby to a point of use in liquid particle form and discharging said particle-laden carrier vehicle from said chamber to the point of use. 